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By requesting 600 time steps, you are asking ANSYS Fluent to compute six pressure cycles. The mass flow rate history is shown in Figure 6.7: Mass Flow Rate History (Transient Flow) (p. 230).

Figure 6.7: Mass Flow Rate History (Transient Flow)

6.Optionally, you can review the effect of dynamic mesh adaption performed during transient flow computation as you did in steady-state flow case.

7.Save the transient case and data files (noz_uns.cas.gz and noz_uns.dat.gz).

File → Write → Case & Data...

6.4.11. Saving and Postprocessing Time-Dependent Data Sets

At this point, the solution has reached a time-periodic state. To study how the flow changes within a single pressure cycle, you will now continue the solution for 100 more time steps. You will use ANSYS Fluent’s solution animation feature to save contour plots of pressure and Mach number at each time step, and the autosave feature to save case and data files every 10 time steps. After the calculation is complete, you will use the solution animation playback feature to view the animated pressure and Mach number plots over time.

1.Request the saving of case and data files every 10 time steps.

Solution → Activities → Autosave

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Setup and Solution

a.Enter 10 for Save Data File Every.

b.Select Each Time for Save Associated Case Files.

c.Retain the default selection of time-step from the Append File Name with drop-down list.

d.Enter noz_anim.gz for File Name.

When ANSYS Fluent saves a file, it will append the time step value to the file name prefix ( noz_anim ). The standard extensions ( .cas and .dat ) will also be appended. By adding the optional extension .gz to the end of the file name, you instruct ANSYS Fluent to save the case and

data files in compressed format. This will yield file names of the form noz_anim-1-00640.cas.gz and noz_anim-1-00640.dat.gz , where 00640 is the time step number.

e.Click OK to close the Autosave dialog box.

Tip

If you have constraints on disk space, you can restrict the number of files saved by ANSYS Fluent by enabling the Retain Only the Most Recent Files option and setting the Maximum Number of Data Files to a nonzero number.

2.Create an animation definition for the nozzle pressure contour plot.

Solution → Activities → Create → Solution Animations...

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a.Enter pressure for the Name.

b.Select Time Step for Record after every.

The default value of 1 in the integer number entry box instructs ANSYS Fluent to update the animation sequence at every time step.

c.Select In Memory from the Storage Type drop-down.

The In Memory option is acceptable for a small 2D case such as this. For larger 2D or 3D cases, saving animation files with either the Metafile or PPM Image option is preferable, to avoid using too much of your machine’s memory.

d.Enter 3 for the Window Id.

e.Click New Object and select Contours... from the drop-down list to open the associated dialog box.

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Setup and Solution

i.Select Pressure... and Static Pressure from the Contours of drop-down lists.

ii.Ensure that Filled is enabled in the Options group box.

iii.Disable Auto Range.

iv.Enter 0.25 atm for Min and 1.25 atm for Max.

v.Click Save/Display and close the Contours dialog box.

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vi. Figure 6.8: Pressure Contours at t=0.017136 s

f.Ensure contour-1 is selected in the Animation Object group box.

g.Click OK to create the animation definition.

3.Create an animation definition for the Mach number contour plot.

Solution → Activities → Create → Solution Animations...

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Setup and Solution

a.Enter mach-number for the Name.

b.Select Time Step for Record after every.

The default value of 1 in the integer number entry box instructs ANSYS Fluent to update the animation sequence at every time step.

c.Ensure that In Memory is selected from the Storage Type drop-down.

d.Enter 4 for the Window Id.

e.Click New Object and select Contours... from the drop-down list to open the associated dialog box.

i.Select Velocity... and Mach Number from the Contours of drop-down lists.

ii.Ensure that Filled is enabled in the Options group box.

iii.Disable Auto Range.

iv.Enter 0.00 for Min and 1.30 for Max.

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v.Click Save/Display and close the Contours dialog box.

vi.Figure 6.9: Mach Number Contours at t=0.017136 s

f.Ensure contour-2 is selected in the Animation Object group box.

g.Click OK to create the animation definition.

4.Continue the calculation by requesting 100 time steps.

By requesting 100 time steps, you will march the solution through an additional 0.0028 seconds, or roughly one pressure cycle.

With the autosave and animation features active (as defined previously), the case and data files will be saved approximately every 0.00028 seconds of the solution time; animation files will be saved every 0.000028 seconds of the solution time.

Solution → Run Calculation → Advanced...

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Setup and Solution

Enter 100 for Number of Time Steps and click Calculate.

When the calculation finishes, you will have ten pairs of case and data files and there will be 100 pairs of contour plots stored in memory. In the next few steps, you will play back the animation sequences and examine the results at several time steps after reading in pairs of newly saved case and data files.

5. Play the animation of the pressure contours.

Results → Animations → Solution Animation Playback Edit...

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a.Select pressure in the Sequences selection list.

b.Click the play button (the second from the right in the group of buttons in the Playback group box).

c.Close the Playback dialog box.

Examples of pressure contours at s (the 630th time step) and s (the 670th time step) are shown in Figure 6.10: Pressure Contours at t=0.017993 s(p. 238) and Figure 6.11: Pressure Contours at t=0.019135 s (p. 239). These contour plots can be shown by seleting frame 30 and 70 in theFrame selector in the Playback dialog box.

Figure 6.10: Pressure Contours at t=0.017993 s

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Figure 6.11: Pressure Contours at t=0.019135 s

6.In a similar manner to steps 4 and 5, select the appropriate active window and animation sequence name for the Mach number contours.

Examples of Mach number contours at s and s are shown in Figure 6.12: Mach Number Contours at t=0.017993 s (p. 239) and Figure 6.13: Mach Number Contours at t=0.019135 s(p. 240).

Figure 6.12: Mach Number Contours at t=0.017993 s

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Figure 6.13: Mach Number Contours at t=0.019135 s

Tip

ANSYS Fluent gives you the option of exporting an animation as an MPEG file or as a series of files in any of the hardcopy formats available in the Save Picture dialog box (including TIFF and PostScript).

To save an MPEG file, select MPEG from the Write/Record Format drop-down list in the Playback dialog box and then click the Write button. The MPEG file will be saved in your working folder. You can view the MPEG movie using an MPEG player (for example, Windows Media Player or another MPEG movie player).

To save a series of TIFF, PostScript, or other hardcopy files, select Picture Frames in the

Write/Record Format drop-down list in the Playback dialog box. Click the Picture Options... button to open the Save Picture dialog box and set the appropriate parameters for saving the hardcopy files. Click Apply in the Save Picture dialog box to save your modified settings. Click Save... to select a directory in which to save the files. In the Playback dialog box, click the Write button. ANSYS Fluent will replay the animation, saving each frame to a separate file in your working folder.

If you want to view the solution animation in a later ANSYS Fluent session, you can select

Animation Frames as the Write/Record Format and click Write.

Warning

Because the solution animation was stored in memory, it will be lost if you exit ANSYS Fluent without saving it in one of the formats described previously. Note that only the animation-frame format can be read back into the Playback dialog box for display in a later ANSYS Fluent session.

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Setup and Solution

7.Read the case and data files for the 660th time step (noz_anim–1–00660.cas.gz and noz_an- im–1–00660.dat.gz) into ANSYS Fluent.

8.Plot vectors at s (Figure 6.14: Velocity Vectors at t=0.018849 s (p. 242)).

Results → Graphics → Vectors → Edit...

a.Ensure Auto Scale is enabled under Options.

b.Enter 10 under Scale.

c.Enter 50 under Skip.

d.Click Display and close the Vectors dialog box.

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